1. Field of the Invention
This invention relates to mufflers, and in particular to high efficiency mufflers arranged to reduce fuel consumption by decreasing back-pressure and therefore load on the engine. The mufflers feature flow-through passages and chambers defined by heat-conducting baffles or partitions that draw energy from the exhaust stream, the passages or chambers being acoustically configured to reduce exhaust noise: (a) by converting kinetic energy of the exhaust stream into heat energy; (b) by isolating and attenuating acoustic waves within the passages or chambers, and/or by partial or complete cancellation of the acoustic waves.
The use of heat conducting baffles or passages enables the mufflers of the preferred embodiments to be used not only for sound reduction, but also for electricity generation. This is accomplished by using the heat carried away by the baffles or partitions to power thermoelectric generators to further increase fuel efficiency. In addition, the heat extracted by the baffles of the flow-through muffler may be used for other purposes such as in a reformer that converts hydrocarbons such as diesel fuel into hydrogen gas.
In addition, in contrast to conventional mufflers, the acoustic characteristics the mufflers of the preferred embodiments may be manually or automatically varied or adapted to achieve a desired acoustic effect, thus enabling the mufflers of the preferred embodiment to be tuned. If automatic adaptation is provided-for, the tuning may be carried out in real time in response to engine load and speed.
According to a further variation, the muffler of the preferred embodiments may include baffles or partitions coated with a catalyst to expedite heat transfer and reduce emissions.
2. Description of Related Art
a. Flow-Through Mufflers
Noise silencing mufflers are well-known and take on a variety of forms. The most commonly-used type incorporates a sound absorbing material through which exhaust gases are passed. However, the material through which the gases are passed inherently cause back-pressure to be exerted on the engine. Excess back-pressure increases fuel consumption and decreases engine performance.
To decrease back-pressure on the engine and increase efficiency, it is also known to provide mufflers which incorporate circuitous passages that isolate and attenuate, or cancel, sound waves generated by the exhaust stream, rather than relying on sound absorbing materials. In order to minimize turbulence or eddy currents that increase back pressure and noise, many of the circuitous passage designs divide the incoming exhaust stream into multiple paths, and converge the paths at the outlet.
Examples of flow-through mufflers with circuitous passages are disclosed in U.S. Pat. Nos. 3,786,896; 4,809,812; 5,444,197; 6,364,054; and 6,296,074. Of particular interest are U.S. Pat. No. 6,364,054, which discloses a muffler having expansion chambers and reduced openings that decrease sound volume by conversion of a part of the sound energy to heat energy, and which modify the frequency of sound passing through the muffler to provide tuning. Also of particular interest are U.S. Pat. No. 6,089,347, in which various dividers and partitions are arranged so that sound is attenuated in the spaces between the partitions as exhaust gases are directed past the outward ends of the partitions, the lengths of the spaces between the partitions being chosen to tune the muffler to affect selected frequencies, and U.S. Pat. No. 6,296,074, which discloses a sound cancelling muffler, in which the exhaust stream is separated into two different passages having different lengths so that at the point of conversion, the acoustic waves generated by the exhaust gases are out of phase and actually cancel as opposed to merely being attenuated.
In its broadest form, the present invention combines the principle of heat conversion taught by the above-cited U.S. Pat. No. 6,364,054 and the sound attenuation or cancellation principles of U.S. Pat. No. 6,089,347, U.S. Pat. No. 6,296,074 and other prior patents in a way that offers a substantially simplified construction, and that enables increased versatility, including the ability to utilize the muffler for electricity generation and even emissions reduction, and to enable the muffler to be tuned to compensate for the different frequencies generated at different engine speeds and loads.
b. Thermo-Electric Heat-to-Electricity Conversion
Instead of simply dissipating the heat carried away by the thermally-conductive baffles or partitions of the flow through muffler of the preferred embodiments, one aspect of the present invention is to utilize the heat for thermoelectric generation. While it is known to convert waste heat into electricity using thermo-electric generation, the present invention combines the thermo-electric generation with noise reduction by utilizing the energy captured by heat-conductive baffles or partitions in the muffler. Since 80% or more of energy consumed by the engine is lost through the exhaust system, this can result in substantial energy savings, while at the same time greatly increasing muffler efficiency without increasing back pressure. By way of background, thermo-electric generation systems for vehicles are described in U.S. patent application Ser. Nos. 11/056,233 and 11/056,237, both filed on Mar. 2, 2005, and in U.S. Pat. Nos. 6,605,773; 6,172,427; 5,968,456; 5,753,383; 5,625,245; 4,753,682; and 4,673,863; and 4,161,657.
c. Tunability
Finally, according to another aspect of the present invention, the attenuation frequencies of the muffler may not only be pre-selected, but the frequency may actually be adjusted during use. A muffler that is “tuned” to attenuate frequencies at racing speeds might have little effect when the race car is pulling into a garage in the middle of the night. The tuning is achieved by using the principle of sound cancellation, but with adjustable divergent paths. No prior muffler has this capability.